Introduce UdpSocketState:try_send API for windows

quinn-udp/src/windows.rs

@@ -124,23 +124,25 @@ impl UdpSocketState {
     }
 
     pub fn send(&self, socket: UdpSockRef<'_>, transmit: &Transmit<'_>) -> io::Result<()> {
-        let rc = send(socket, transmit);
+        match send(socket, transmit) {
+            Ok(()) => Ok(()),
+            Err(e) if e.kind() == io::ErrorKind::WouldBlock => Err(e),
+            Err(e) => {
+                // Other errors are ignored, since they will usually be handled
+                // by higher level retransmits and timeouts.
+                // - PermissionDenied errors have been observed due to iptable rules.
+                //   Those are not fatal errors, since the
+                //   configuration can be dynamically changed.
+                // - Destination unreachable errors have been observed for other
+                log_sendmsg_error(&self.last_send_error, e, transmit);
 
-        if rc != 0 {
-            let e = io::Error::last_os_error();
-            if e.kind() == io::ErrorKind::WouldBlock {
-                return Err(e);
+                Ok(())
             }
-
-            // Other errors are ignored, since they will usually be handled
-            // by higher level retransmits and timeouts.
-            // - PermissionDenied errors have been observed due to iptable rules.
-            //   Those are not fatal errors, since the
-            //   configuration can be dynamically changed.
-            // - Destination unreachable errors have been observed for other
-            log_sendmsg_error(&self.last_send_error, e, transmit);
         }
-        Ok(())
+    }
+
+    pub fn try_send(&self, socket: UdpSockRef<'_>, transmit: &Transmit<'_>) -> io::Result<()> {
+        send(socket, transmit)
     }
 
     pub fn recv(
@@ -272,7 +274,7 @@ impl UdpSocketState {
     }
 }
 
-fn send(socket: UdpSockRef<'_>, transmit: &Transmit<'_>) -> i32 {
+fn send(socket: UdpSockRef<'_>, transmit: &Transmit<'_>) -> io::Result<()> {
     // we cannot use [`socket2::sendmsg()`] and [`socket2::MsgHdr`] as we do not have access
     // to the inner field which holds the WSAMSG
     let mut ctrl_buf = cmsg::Aligned([0; CMSG_LEN]);
@@ -349,7 +351,7 @@ fn send(socket: UdpSockRef<'_>, transmit: &Transmit<'_>) -> i32 {
     encoder.finish();
 
     let mut len = 0;
-    unsafe {
+    let rc = unsafe {
         WinSock::WSASendMsg(
             socket.0.as_raw_socket() as usize,
             &wsa_msg,
@@ -358,7 +360,13 @@ fn send(socket: UdpSockRef<'_>, transmit: &Transmit<'_>) -> i32 {
             ptr::null_mut(),
             None,
         )
+    };
+
+    if rc != 0 {
+        return Err(io::Error::last_os_error());
     }
+
+    Ok(())
 }
 
 fn set_socket_option(